It has been revealed that serotonin 5-HT.sub.3 receptor antagonists can inhibit nausea and emesis as side effects caused by the use of cisplatin and the like carcinostatic agents and by radiation treatments, and several compounds thereof are now used in the clinical field. In addition to this, development on their use as digestive organ function controlling drugs has recently been examined.
The inventors of the present invention have already found that certain benzoxazole derivatives are possessed of serotonin 5-HT.sub.3 receptor antagonism (JP-A-6-345744; the term "JP-A" as used herein means an "unexamined published Japanese patent application").
When a compound having only serotonin 5-HT.sub.3 receptor antagonism is administered as a digestive organ function controlling drug, it can inhibit diarrhea but poses a problem of frequently causing constipation as a side effect.